U.S. patent number 7,356,335 [Application Number 10/866,756] was granted by the patent office on 2008-04-08 for wireless communication apparatus.
This patent grant is currently assigned to Oki Electric Industry Co., Ltd.. Invention is credited to Hiroyuki Akiyama.
United States Patent |
7,356,335 |
Akiyama |
April 8, 2008 |
Wireless communication apparatus
Abstract
A wireless communication apparatus coordinates communication
among a set of mobile stations by giving the mobile stations
permission to transmit packets. The mobile stations divide
comparatively long packets into shorter fragment packets. When the
wireless communication apparatus receives a fragment packet with an
indication that the station that transmitted the fragment packet
has another fragment packet to transmit, the wireless communication
apparatus gives the mobile station permission to transmit the next
packet. The mobile station can accordingly transmit its fragment
packets in continuous succession, avoiding a defragmentation
timeout at the receiving end.
Inventors: |
Akiyama; Hiroyuki (Tokyo,
JP) |
Assignee: |
Oki Electric Industry Co., Ltd.
(Tokyo, JP)
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Family
ID: |
34373411 |
Appl.
No.: |
10/866,756 |
Filed: |
June 15, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050070270 A1 |
Mar 31, 2005 |
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Foreign Application Priority Data
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Sep 30, 2003 [JP] |
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2003-340646 |
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Current U.S.
Class: |
455/424; 370/343;
370/449; 370/455 |
Current CPC
Class: |
H04W
74/04 (20130101); H04W 28/06 (20130101); H04W
28/24 (20130101) |
Current International
Class: |
H04Q
7/20 (20060101) |
Field of
Search: |
;455/414.1,502,507,424
;370/248,389,338,348,349,414,418,350,229,445,343,455,449
;375/145 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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4-090230 |
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Mar 1992 |
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JP |
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2002-300175 |
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Oct 2002 |
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JP |
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2003-179610 |
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Jun 2003 |
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JP |
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Other References
Notice of Reason for Rejection dated Mar. 7, 2006. cited by
other.
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Primary Examiner: Gelin; Jean
Assistant Examiner: Vu; Michael T
Attorney, Agent or Firm: Nixon Peabody LLP Studebaker;
Donald R.
Claims
What is claimed is:
1. A wireless communication apparatus having a point coordination
function for performing centralized control over access to a
wireless medium used by a basic service set of mobile stations by
giving the mobile stations permission to transmit packets, the
mobile stations divide packets into fragment packets and transmit
all but the last of the fragment packets with a more fragments
indication indicating that there are more fragment packets to be
transmitted, comprising: an input communication unit for input of
packets received from the mobile stations; an outgoing packet input
unit for receiving packet body data to be transmitted; an outgoing
address input unit for receiving a first address designating a
first one of the mobile stations to which the packet body data are
to be transmitted; an analyzer for analyzing information in the
received packets to determine at least whether the mobile stations
that transmitted the packet have more packets to transmit by
checking the more fragments indication, and outputting analysis
results, and the analyzer outputs a second address indicating a
second one of the mobile stations, from which the received packet
was received, a packet generator for generating outgoing packets
according to the analysis results, the packet generator including
said second address in the contention-free polling packet, whereby
the polling packet is sent to the second one of the mobile
stations; a timing controller for controlling the transmission
timing of the outgoing packets; and a packet output unit for output
of the outgoing packets at the designated transmission timing;
wherein if one of the mobile stations transmits a packet with an
indication that it has another packet to transmit, the packet
generator generates a contention-free polling packet addressed to
said one of the mobile stations, the contention-free polling packet
giving said one of the mobile stations permission to transmit a
next packet, and the packet output unit outputs the contention-free
polling packet as one of the outgoing packets, before polling
another one of the mobile stations.
2. The wireless communication apparatus of claim 1 wherein the more
fragments indication comprises a bit in a packet header.
3. The wireless communication apparatus of claim 1, wherein: the
packet generator compares the first address with the second
address; and if the first address and the second address are
identical, the packet generator includes said packet body data in
the contention-free polling packet.
4. The wireless communication apparatus of claim 1, wherein the
packet generator omits said packet body data from the
contention-free polling packet if the first address does not match
the second address.
5. The wireless communication apparatus of claim 1, wherein if the
outgoing packet input unit receives said packet body data when the
input communication unit receives a packet from one of the mobile
stations and the analyzer determines that said one of the mobile
stations does not have another packet to transmit, the packet
generator generates a packet including the first address and said
packet body data.
6. The wireless communication apparatus of claim 4, further
comprising a polling request input unit for input of a polling
request signal, wherein if the polling request input unit receives
said polling request signal and the outgoing packet input unit
receives said packet body data when the input communication unit
receives said packet from said one of the mobile stations and the
analyzer determines that said one of the mobile stations does not
have another packet to transmit, the packet generator generates a
packet including said the first address, said packet body data, and
a polling indication giving said first one of the mobile stations
permission to transmit said next packet.
7. The wireless communication apparatus of claim 1, wherein the
wireless communication apparatus functions as an access point.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to wireless communication apparatus
operating, for example, as an access point performing centralized
control over a wireless communication area, more particularly to an
apparatus with features that enable mobile stations to transmit
fragment packets in a continuous series.
2. Description of the Related Art
Local area networks using wired transmission media have often
employed the CSMA/CD (Carrier Sense Multiple Access with Collision
Detection) communication protocol to enable a plurality of terminal
devices to transmit packets on a shared medium. CSMA/CD has been
standardized by the Institute of Electrical and Electronics
Engineers (IEEE) as IEEE standard 802.3 for media access in wired
communication equipment. To transmit a packet, terminal equipment
implementing the CSMA function senses the usage status of the
medium and transmits the desired packet after confirming that the
medium has been idle for a certain length of time.
Wired communication equipment implementing the CD function
continues to sense the medium even after transmitting a packet. If
the transmitted packet collides with a packet transmitted from
another source, the wired communication equipment detects the
collision and transmits the same packet again after a random time
interval referred to as a back-off interval. The random back-off
interval reduces the probability of another collision between
retransmitted packets. The methods used for sensing the carrier and
detecting collisions depend on technology which is only feasible in
a wired communication environment, however, so a different protocol
is necessary in a wireless communication environment.
One protocol suitable for a wireless communication environment is
CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). A
version of CSMA/CA appears as a distributed coordination function
(DCF) in IEEE standard 802.11, which concerns wireless local area
networks. Wireless communication apparatus implementing the IEEE
802.11 distributed coordination function senses the medium before
transmitting a packet, temporarily defers packet transmission if
the medium is busy, waits for the medium to become idle, then waits
for a further length of time equal to a fixed interval plus a
random back-off interval, and transmits the packet if the medium
remains idle during this further length of time. The fixed interval
ensures a minimum spacing between transmitted packets; the random
back-off interval reduces the probability of collisions between
packets.
IEEE standard 802.11 also specifies a point coordination function
(PCF) in which a single base station, referred to as an access
point, controls communication among a set of mobile stations
referred to as a basic service set (BSS). When the point
coordination function is used, the access point has an independent
right to transmit packets on the wireless communication medium to
the stations in its BSS, but these stations cannot transmit packets
without permission from the access point. Such permission is given
a packet at a time in a process referred to as contention-free (CF)
polling, by sending control information referred to as a
CF-Poll.
When the access point has an outgoing packet of data to send to
another station, it can transmit the packet and simultaneously poll
the other station by setting CF-Poll information in the packet
header. Alternatively, the access point can poll any station in the
BSS by sending the station a packet including a CF-Poll with no
packet body data. The access point maintains a list of CF-Pollable
stations and polls these stations one at a time in their order on
the list. The station that receives a CF-Poll from the access point
can transmit the next packet after waiting for a comparatively
short fixed interval, to which no random back-off interval is
added.
The interval between packets transmitted under the point
coordination function is accordingly shorter than the interval
between packets transmitted under the distributed coordination
function. This feature gives PCF transmission priority over DCF
transmission. A CF-Poll, however, allows the polled station to
transmit only one packet. A station cannot transmit a continuous
series of packets unless it receives a continuous series of
CF-Polls.
By having the access point control all packet transmission within a
BSS, the point coordination function improves communication
efficiency, as compared with the distributed coordination function,
because all collisions between transmitted packets are avoided, and
because the intervals between transmitted packets are shorter.
Further information can be found in Japanese Unexamined Patent
Application Publication No. 2002-300175, and in `Wireless LAN
Medium Access Control (MAC) and Physical Layer (PHY)
Specifications`, ANSI/IEEE Standard 802.11, 1999 Edition.
Incidentally, the term `packet` as used herein is synonymous with
the term `frame` used in the IEEE standard.
IEEE standard 802.11 also designates fragmentation and
defragmentation functions. The fragmentation function divides a
packet into a plurality of shorter fragment packets and transmits
the fragment packets. The fragmentation function makes the
retransmission of packets in which a bit error occurs during
transmission more efficient, because only one fragment of the
packet has to be retransmitted. The defragmentation function
reassembles the fragment packets to reconstruct the original
packet. Since it may not be possible to receive all of the fragment
packets constituting the original packet, a defragmentation timeout
limit (MaxReceiveLifetime) is set as a parameter of the
defragmentation function. A timer at the receiving station is
started at the reception of the first fragment packet. If the
reconstruction of the original packet is not completed within the
timeout limit, the receiving station discards the packet.
When the fragmentation and defragmentation functions are used with
distributed coordination, a mobile station does not need to receive
permission from the access point to transmit packets, so it can
transmit a plurality of fragment packets in a continuous series.
More accurately, the fragment packets and the answering
acknowledgment packets from the receiving station alternate with
one another in a continuous series. This capability is guaranteed
by a provision in IEEE standard 802.11 that lets a station omit the
random back-off interval after transmitting a fragment packet.
Normally this allows all fragment packets to be received within the
defragmentation timeout limit.
When the fragmentation and defragmentation functions are used with
point coordination, however, a problem occurs. Because a mobile
station receives permission to transmit only one fragment packet at
a time, and because permission is granted according to a polling
list, there is no guarantee that a station with fragment packets to
transmit will be able to transmit the fragment packets in a
continuous series. Normally, the station will not be able to do so,
because the access point must poll all of the stations on its
polling list before it can send a consecutive series of CF-Polls to
any one station. A station that receives a fragment packet
transmitted under PCF control may therefore have to wait for a
considerable time before receiving the next fragment packet, making
defragmentation timeout a significant problem during PCF
periods.
SUMMARY OF THE INVENTION
An object of the present invention is to provide wireless
transmission apparatus to which mobile stations can transmit
fragment packets in a continuous series despite the use of a
high-efficiency communication function such as a point coordination
function.
The invented wireless transmission apparatus controls access to a
wireless communication medium by a set of mobile stations. The
apparatus includes an input communication unit for input of packets
received from the mobile stations, an analyzer for analyzing
information in the received packets, a packet generator for
generating outgoing packets according to the results of the packet
analysis, a timing controller for controlling the transmission
timing of the outgoing packets, and a packet output unit for output
of the outgoing packets at the designated transmission timing. The
packet generator recognizes, from the packet analysis results,
whether a mobile station that has transmitted a fragment packet
has: another fragment packet to transmit, and if it does, generates
an outgoing packet giving the mobile station permission to transmit
the next packet on the wireless communication medium, with priority
over other mobile stations.
In analyzing a received packet, the analyzer checks, for example, a
bit in the packet header to determine whether the mobile station
that transmitted the packet has an additional fragment packet to
transmit.
The apparatus may also include an outgoing packet input unit for
input of packet body data to be transmitted to a mobile station at
a first address, and an address input unit for input of the first
address. When the analyzer analyzes a received packet, it provides
the packet generator with a second address, this being the address
of the mobile station that transmitted the received packet. If the
first address is identical to the second address, the packet
generator generates an outgoing packet addressed to the second
address, including permission to transmit the next packet and
including the packet body data received from the outgoing packet
input unit; if the first address differs from the second address,
the packet generator generates an outgoing packet addressed to the
second address, including permission to transmit the next packet
but not including the packet body data received from the outgoing
packet input unit.
The apparatus preferably also includes a polling request input unit
for input of a polling request signal. When the analyzer decides,
by analyzing the received packet, that the mobile station that
transmitted the packet has no further fragment packet to transmit,
if the outgoing packet input unit has received packet body data and
the address input unit has received a first address, the packet
generator generates an outgoing packet including the first address
and the packet body data. If the polling request input unit
receives a polling request signal at this time, the packet
generator adds a polling indication to the outgoing packet, thereby
giving the mobile station at the first address permission to
transmit the next packet on the wireless medium.
Upon receiving a fragment packet including an indication that there
is another fragment to follow, the invented wireless communication
apparatus automatically gives the mobile station that transmitted
the fragment packet permission to transmit the next packet. The
invented wireless communication apparatus therefore allows a mobile
station to transmit to transmit a plurality of fragment packets in
a consecutive series, even while a point coordination function or
other high-efficiency communication function is in use. The mobile
station that receives the fragment packets can receive them in a
substantially continuous series, avoiding a defragmentation
timeout.
BRIEF DESCRIPTION OF THE DRAWINGS
In the attached drawings:
FIG. 1 illustrates communication in a basic service set;
FIG. 2 is a block diagram showing an example of the structure of
the access point in FIG. 1;
FIG. 3 is a block diagram showing an example of the internal
structure of the communication controller in FIG. 2 according to
the present invention;
FIG. 4 illustrates the structure of a packet with a header
conforming to the IEEE standard 802.11;
FIG. 5 illustrates packet transmission during a PCF period;
FIG. 6 illustrates fragment packet transmission during a PCF
period;
FIGS. 7 and 8 illustrate transmission control by the access
point;
FIG. 9 is a flowchart showing decisions and operations carried out
in the outgoing packet generation processing unit in FIG. 3 during
the control sequences in FIGS. 7 and 8;
FIG. 10 illustrates packet transmission during a DCF period;
and
FIG. 11 illustrates fragment packet transmission during a DCF
period.
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of the invention will now be described with
reference to the attached drawings, in which like elements are
indicated by like reference characters. Reference characters of
signal lines will also be used to denote the signals carried on the
signal lines.
Referring to FIG. 1, the preferred embodiment is used in an access
point (AP) 10 operating as a base station for a basic service set
(BSS) 12 of mobile stations (STA) 14 that communicate with each
other and with the outside world through the access point 10. After
communication links have been established between the mobile
stations 14 and the access point 10, the access point 10 and the
mobile stations 14 constitute a piconet having an infrastructure
network configuration.
Referring to FIG. 2, the access point 10 has a wireless
communication unit 20 that modulates and demodulates
radio-frequency (RF) signals and performs baseband (BB) processing.
The signals are transmitted and received by using a spread-spectrum
communication system or an orthogonal frequency division
multiplexing (OFDM) communication system. The access point 10 also
has a communication control unit 22 that processes transmitted and
received packets and controls the transmission and reception of
data according to a communication protocol, an interface (I/F) unit
24 that connects the access point 10 to the Internet or another
wired network, and a system control unit 26 that performs overall
control of the access point 10.
An example of the internal structure of the communication control
unit 22, which performs media access control processing, is shown
in FIG. 3. The communication control unit 22 has a received packet
analyzer 30, which analyzes received packets. The received packet
analyzer 30 is a processor for analyzing the packet headers of
packets conforming to IEEE standard 802.11, which are received on
an input signal line 32. The received packet analyzer 30 also
receives a DCF/PCF switching signal on another input signal line
34, and operates in either the DCF mode or the PCF mode according
to this switching signal. When the DCF/PCF switching signal
indicates the PCF mode, the received packet analyzer 30 determines
whether the station from which the current packet was received has
another fragment packet to transmit by checking a More Fragments
bit in the header of the received packet, outputs a More Fragments
bit detection result signal on an output signal line 36, and
outputs an address signal on another output signal line 38,
indicating the source address of the packet, that is, the address
of the station from which the packet was received.
The packet structure specified in IEEE standard 802.11 is shown in
FIG. 4. The packet consists of a media access control (MAC) header,
a frame body, and a frame check sequence (FCS). The More Fragments
(More Frag) bit is the eleventh bit (bit B10) in the two-octet (2
oct) frame control field of the MAC header. The More Fragments bit
is set to `1` to indicate the existence of another fragment packet
following the present packet. Bits B2-B7 in the frame control field
are a type and sub-type designation indicating, among other things,
whether the station 14 that receives the packet has permission to
transmit the next packet (CF-Poll). When this permission is given,
the station 14 may transmit any packet that it holds, not
necessarily a fragment packet.
The received packet analyzer 30 also determines, from the packet
header, whether the received packet should be transmitted to
another station. If the received packet is to be transmitted to
another station, the received packet analyzer 30 outputs the
received packet on an output signal line 40 which is connected to
an outgoing packet input unit 42 as shown in FIG. 3.
A received packet phase counter 50 receives a received packet
enable signal, which indicates the temporal position or `phase` of
the received packet, on an input signal line 52, and counts in
synchronization with the phase of the received packet to obtain a
phase count value, which is output on an output signal line 54.
This output signal line 54 is connected to the received packet
analyzer 30, an outgoing packet generator 60, and a transmit timing
controller 64. The received packet analyzer 30 recognizes the
locations of the More Fragments bit and source address in the
received packet according to the phase count value output from the
received packet phase counter 50.
The outgoing packet generator 60 is connected to the outgoing
packet input unit 42 for input of packet body data to be
transmitted, an outgoing address input unit 44 for input of the
destination address of the packet body data, a CF-Poll request
input unit 46 for input of a CF-Poll request signal indicating
whether to add permission to transmit the next packet (CF-Poll) to
a packet when the packet is transmitted to the wireless
communication medium, and an outgoing packet enable signal input
unit 48 for input of an outgoing packet enable signal. These
signals are generated externally. From these signals, together with
the More Fragments bit detection result signal 36 and address
signal 38 output from the received packet analyzer 30 and the phase
count value 54, the outgoing packet generator 60 generates a packet
conforming to IEEE standard 802.11, and outputs the generated
packet on an output signal line 62.
The transmit timing controller 64 receives the phase count value 54
from the received packet phase counter 50, and counts out the
transmission timing of the packet on an output signal line 66. The
transmit timing controller 64 starts counting after the phase count
value 54 has reached `15`, at the time of completion of input of
the received packet. In the present embodiment, the transmit timing
controller 64 signals the transmission timing by counting up to `7`
as shown in FIGS. 7 and 8. An outgoing packet timing controller 70
connected to the transmit timing signal line 66 receives the
outgoing packet generated in the outgoing packet generator 60 on
signal line 62, and outputs the outgoing packet on an output signal
line 72 at the transmission timing phase signaled by the transmit
timing controller 64.
An example of normal packet transmission control with point
coordination performed by the communication control unit 22 will be
described with reference to FIG. 5. An outgoing packet 500
addressed to station A (STA_A), including packet body data (pkt)
and permission to transmit the next packet (CF-Poll), is
transmitted from the access point 10 and received by station A.
After receiving the outgoing packet 500, station A waits for a
fixed interval, then transmits a packet 502 including the address
(AP) of the access point 10, an acknowledgement (ACK), and packet
body data (pkt). The access point 10 may now poll another station B
(STA_B) by transmitting a packet 504 addressed to station B,
including permission to transmit the next packet (CF-Poll). Station
B receives the CF-Poll packet 504, and after a fixed interval,
transmits a packet 506 including the address (AP) of the access
point and packet body data (pkt).
Fragment packet transmission under point coordination control will
be described with reference to FIG. 6. In this drawing a packet
transmitted from station A (STA_A) to the access point 10 is
divided into three fragment packets. When the access point polls
station A by sending it a packet 600 including permission to
transmit the next packet (CF-Poll), station A assembles a packet
601 including the address AP of the access point and the first
fragment (1st FRAG) of the original packet, sets the More Fragments
bit in the assembled packet to `1` (F1), and transmits the
assembled packet 601. The access point 10 recognizes that the More
Fragments bit is set to `1` (F1) and polls station A again by
transmitting a packet 602 to station A, once more giving permission
to transmit the next packet (CF-Poll). Station A receives this
second polling packet 602, assembles another packet 603 with the
More Fragments bit set to `1` (F1), including the address of the
access point and the second fragment of the original packet, and
transmits the assembled packet 603. When the access point 10
recognizes that the More Fragments bit is set to `1` (F1) in this
packet 603, it transmits another CF-Poll packet 604 addressed to
station A, giving station A permission to transmit the next packet
again. Station A assembles a packet 605 including the address of
the access point and the third fragment of the original packet,
with the More Fragments bit set to `0` (F0) to indicate that there
are no remaining fragment packets, and transmits the assembled
packet 605.
As described above, the present invention enables a mobile station
14 to transmit fragment packets continuously to the access point
10, even during a PCF period. During PCF control, the access point
10 analyzes each packet received from the station 14, recognizes
from the More Fragments bit whether there is another fragment
packet, and if there is, gives the station 14 permission to
transmit the next packet. Continuing in like manner, the access
point sends the same station a continuous series of CF-Poll packets
as long as it continues to receive packets with the More Fragments
bit set to `1`.
Transmission control by the access point 10 will now be described
in more detail with reference to FIG. 7. It is assumed that the
DCF/PCF switching signal 34 input to the received packet analyzer
30 as shown in FIG. 3 has selected the PCF mode and the received
packet analyzer 30 has been activated. A packet 700 is transmitted
from station A (STA_A) 14, received at the access point 10, and
input to the received packet analyzer 30. The header of received
packet 700 includes the address (AP) of the access point 10 and a
More Fragments bit set to `1` (Frg1); the header is followed by the
first fragment of the original packet.
A received packet enable signal 52 indicating the phase of received
packet 700 is input to the received packet phase counter 50.
Triggered by the received packet enable signal, the received packet
phase counter 50 starts counting synchronously from `1` to `15`
during the input of the received packet enable signal 52. The
received packet analyzer 30 outputs the results of its analysis of
the received packet header on its output signal lines 36 and 38 at
the timing of phase count `2`. The analysis results show that the
More Fragments bit is set to `1`, indicating the existence of
another fragment packet at station A, and that the source address
(ADDR) is the address of station A. These results are sent to the
outgoing packet generator 60, which recognizes the information in
them.
The outgoing packet generator 60 also receives the packet body data
of next packet to transmit, which is input to the outgoing packet
input unit 42, the outgoing packet enable signal input to the
outgoing packet enable signal input unit 48, the CF-Poll request
signal input to the CF-Poll request input unit 46, and the
destination address input to the outgoing address input unit 44.
The destination address is the address of the station (STA_A) that
transmitted the received packet 700.
The outgoing packet generator 60 assembles a packet with a header
including CF-Poll information and including the address of station
A as its destination address, followed by the packet body data
received from the outgoing packet input unit 42, which is destined
for the same station A. The assembled packet is output to the
outgoing packet timing controller 70, where it is temporarily
held.
The end of input of the received packet enable signal causes the
transmit timing controller 64 to start its transmission timing
counter (not shown in the drawings). After a fixed interval in
which the transmission timing counter counts from `1` to `7`, the
outgoing packet timing controller 70 outputs the outgoing packet
that it holds on the output signal line 72. The packet includes
CF-Poll information by which the access point 10 gives station A
the right of access to the wireless communication medium.
If the outgoing address input unit 44 designates the address of
station B, which differs from the source station (station A) of the
packet received at this time, the outgoing packet generator 60
assembles a CF-Poll packet addressed to station A, without adding
the outgoing packet input to the outgoing packet input unit 42,
which is addressed to station B, and outputs the assembled packet
to the outgoing packet timing controller 70, as shown in FIG. 8. As
a result, the packet is transmitted with a header including CF-Poll
information and the address of station A as its destination
address, but with no packet body data.
The decisions and operations carried out in the outgoing packet
generator 60 will be described with reference to the flowchart in
FIG. 9. These operations start at a timing determined by the phase
count 54 (in FIG. 3).
In step S900, the outgoing packet generator 60 decides whether the
More Fragments bit in the received packet is set to `1`. If the
More Fragments bit is set to `1`, the process goes to step S902; if
the More Fragments bit is set to `0`, the process goes to step
S904.
If the More Fragments bit is set to `1`, then in steps S902, S906,
S908, S910, and S912, the access point 10 performs operations to
transmit another CF-Poll packet, so that the station 14 which has
transmitted the received packet can transmit the next fragment
packet without delay; if the More Fragments bit is set to `0`, then
in steps S904, S914, S916, and S918, a process is performed for
generating an outgoing packet from information received from the
outgoing packet input unit 42, the outgoing address input unit 44,
and the CF-Poll request input unit 46.
In step S902, the address 38 of the source station of the received
packet is compared with the address obtained from the outgoing
address input unit 44. If the two addresses are identical, the
process goes to step S906, and the packet body data input to the
outgoing packet input unit 42 is selected and received by the
outgoing packet generator 60.
In step S908, an outgoing packet is generated with packet body data
received from the outgoing packet input unit 42, and with a header
including the source address 38 obtained by analysis of the input
packet. The packet header also includes CF-Poll information. FIG. 7
shows a packet including data addressed to station A (STA_A) being
generated and output in this way.
If it is found in step S902 that the source address of the received
packet differs from the address from the outgoing address input
unit 44, then in step S910, which selects the next packet to
transmit, no packet body data is included and the process goes to
step S912. In step S912, the outgoing packet generator 60 generates
an outgoing packet with a header including the recognized address
38 of the source station of the received packet and a CF-Poll, but
with no packet body data. FIG. 8 shows a packet without packet body
data, addressed to station A (STA_A), being generated and output in
this way.
If it is found in step S900 that the More Fragments bit is set to
`0`, then in step S904, the outgoing packet generator 60 selects
the packet body data from the outgoing packet input unit 42 as the
next packet to transmit. In step S914, another decision is made on
the signal received from the CF-Poll request input unit 46. If a
CF-Poll request signal is input, the process goes to step S916; if
a CF-Poll request signal is not input, the process goes to step
S918.
In step S916, the outgoing packet generator 60 generates an
outgoing packet with a header including the address received from
the outgoing address input unit 44 and a CF-Poll, and with packet
body data received from the outgoing packet input unit 42.
If it is found in step S914 that a CF-Poll request is not received
from the CF-Poll request input unit 46, then in step S918, the
outgoing packet generator 60 generates an outgoing packet with a
header including the address received from the outgoing address
input unit 44, but not including a CF-Poll, and with packet body
data received from the outgoing packet input unit 42.
The outgoing packet generated in the outgoing packet generator 60
as described above is temporarily held in the outgoing packet
timing controller 70, and output on the output signal line 72 when
the transmit timing controller 64 provides a transmission-timing
signal at a fixed timing. After the outgoing packet is sent from
the communication control unit 22 to the wireless communication
unit 20, baseband processing is performed, the outgoing packet is
modulated onto a spread spectrum signal channel, and the modulated
signal is transmitted from an antenna.
FIG. 10 illustrates conventional packet transmission control when
two stations in the same BSS 12 communicate with each other
directly, using the distributed coordination function on an ad hoc
network basis, instead of communicating through the access point
10. The two stations are designated station A (STA_A) and station B
(STA_B). FIG. 11 illustrates a similar communication sequence with
fragment packets.
Referring to FIG. 10, during a DCF period as specified in IEEE
standard 802.11, each packet transmission is followed by the return
of an acknowledging (ACK) packet. The ACK packet is separated by a
fixed idle interval from the packet it acknowledges. The next
packet to be transmitted is separated from the ACK packet
transmission by a variable interval in which a random back-off
interval is added to the fixed interval. This random interval
limits the efficiency of communication by the DCF function.
Referring to FIG. 11, during the DCF period, fragment packets can
be transmitted and received without the random back-off interval,
but only when the stations 14 communicate with each other directly.
Accordingly, a BSS environment in which the stations 14 can
communicate with each other directly is required; the stations 14
cannot pass fragment packets through the access point 10.
The conventional PCF function does not give a station 14 the
guaranteed control over the access point 10 needed to transmit
fragment packets to the access point 10 continuously. Therefore, a
defragmentation timeout may occur at the receiving station. The
invented wireless transmission apparatus, however, enables a
station 14 to transmit fragment packets continuously and reliably
through the access point 10 by decisions and packet generation
carried out in the outgoing packet generator 60.
In the wireless transmission apparatus described above, the
invention is applied to an access point implementing the point
coordination function specified in IEEE standard 802.11 to control
media access, but the invention is not limited to this type of
access point. The invention can also be applied, for example to a
quality-of-service (QoS) enhanced access point (QAP) having the
hybrid coordination function (HCF) specified in IEEE standard
802.11e.
Those skilled in the art will recognize that further variations are
possible within the scope of the invention, which is defined in the
appended claims.
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